The present invention relates in general to a self-contained device capable of either heating or cooling an enclosed space to maintain it at a predetermined temperature. In particular, the present invention is directed to a window-mounted room air conditioner of the heat pump type operable to maintain a predetermined indoor room temperature over a wide range of outdoor ambient temperatures.
Self-contained heat pump type room air conditioners are known. U.S. Pat. Nos. 4,102,391; 4,024,722; 3,537,509; 3,373,800; 3,159,981 and 2,847,190 illustrate such prior art devices. Such heat/cool air conditioners include a refrigerant compressor, an indoor heat exchange coil, an outdoor heat exchange coil, and a reversing valve. The compressor, coils, and valve are interconnected in series to provide a conventional reverse cycle refrigeration system.
In a cooling mode of operation, with the reversing valve in a first position, refrigerant circulating in a first direction through the inside coil expands or evaporates to extract heat from the room air, such extracted heat being expelled to the outside ambient air by the outside coil operating as a condenser. In a heating or heat pump mode of operation, with the reversing valve in a second position, refrigerant circulating in a second or reverse direction through the inside coil condenses to provide or give off heat to the room air, such provided heat being extracted from the outside ambient air by the outside coil operating as an evaporator. An indoor fan and an outdoor fan, often rotated by means of a common motor, respectively circulate outdoor ambient air over the outside coil and indoor room air of the inside coil to maximize heat exchange between the coils and outdoor/indoor air.
At low outdoor ambient temperatures (less than 35.degree. F., for example) the ability of the reverse cycle refrigerator system, operating in its heat pump mode to provide heat to the room air, decreases to the point wherein an electrical resistance type heater, located in the path of room air flowing over the inside coil, must be used to replace the heat provided by the reverse cycle refrigeration system which is disabled until the outside ambient temperature rises to a level (e.g., 35.degree. F.) that permits efficient heat pump operation.
A heat/cool room air conditioner of the subject type, as opposed to a larger whole house or central heat pump system, is sold in retail outlets as an owner-installed home appliance. It is well known that the home appliance industry is extremely cost-competitive. Thus, a heat/cool room air conditioner must be produced and sold at a relatively low cost while being efficient from an energy usage standpoint. In designing a heat/cool room air conditioner, care must be taken to provide maximum energy efficiency over the wide range of outdoor ambient temperatures that such heat/cool air conditioner must operate. However, in designing such a system for maximum energy efficiency, manufacturing costs must be kept as low as possible so that the resultant heat/cool air conditioner can be competitively priced at the retail sales level.